1. Field of the Invention
The present invention relates to a control technique of shake compensation configured to prevent image deterioration by compensating for image shake caused by vibration resulting from camera shake, or the like.
2. Description of the Related Art
All the principal imaging operations of contemporary cameras such as determining exposure, or focus adjustment have been automated. Furthermore a camera that includes a shake compensation control apparatus configured to prevent image shake due to camera shake or the like almost completely eliminates factors that result in an imaging error by a photographer.
In this context, a shake compensation control apparatus will be briefly described. Camera shake is normally characterized by a vibration having a frequency of 1 to 10 Hz. It is necessary to detect shaking (rotational shake) of the camera resulting from camera shake and move an image shake compensation lens (hereinafter referred to as a “shake compensation lens (image blur correction lens)”) in response to a detection value in order to enable imaging that eliminates image shake even when camera shake occurs during shutter release. That process requires accurate detection of camera vibration and compensation of variation in the optical axis due to shaking. In principle, image shake can be suppressed by mounting a vibration detection unit configured to acquire a detection result such as the rotational velocity of the shaking and a drive control unit configured to displace the shake compensation lens (image blur correction lens) based on a calculation processing result.
A variety of optical devices include a shake compensation control apparatus that is configured to detect rotational shake using a rotational velocity meter and move a portion of an imaging lens or imaging element to thereby reduce image shake. However, when imaging at a close range (imaging conditions associated with a high imaging magnification), it is not possible to ignore image deterioration caused by vibration that cannot be detected only using a rotational velocity meter, that is to say, shaking that is applied in a horizontal or vertical direction in a plane that is orthogonal to the optical axis of the camera, in other words, so-called translational shake. For example, macro-imaging by approaching to about 20 cm of the object to be imaged requires active detection and compensation of translational shake. It is also necessary to detect and compensate translational shake during imaging under conditions when the focal distance of the imaging optical system is extremely large (for example, 400 mm) even when the object to be imaged is positioned at a distance of approximately one meter from the camera.
The technique disclosed in Japanese Patent Application Laid-Open No. 7-225405 is configured to calculate translational shake by application of double integration to the acceleration detected by an acceleration meter and thereby drive a shake compensation unit by including the output of a separately provided rotational velocity meter.
However, the output of the acceleration meter used in the detection of translational shake exhibits a tendency to be affected by environmental fluctuation such as disturbances, noise or temperature change. Consequently high accuracy compensation of translational shake is difficult since the effect of these unstable factors is further increased by double integration of the detected acceleration. Japanese Patent Application Laid-Open No. 2010-25962 discloses calculation of translational shake by treating translational shake as rotational shake when there is a center of rotation at a position separated from the camera. This method executes shake compensation by providing a rotational velocity and an acceleration meter and using the output of those meters to calculate a compensation value and an angle using a rotation radius of the rotational shake. Unstable factors resulting from an acceleration meter as described above can be mitigated by calculation of a rotation center and limiting to frequency bands in which the effect of disturbances is low.
Compensation of translational shake by shake compensation is associated with the following conditions as a result of the large difference in the shake amount to be compensated on the image surface due to the difference resulting from whether the object to be imaged is imaged at a close range or imaged at a long range (that is to say, the difference in the imaging magnification).
An electronic view finder (EVF) image that is continuously imaged by causing a display apparatus attached to an image capturing apparatus to function as an EVF includes the function of using an image processing technique to execute continuous focusing with an auto-focus (AF) process. This processing is termed a continuous AF function. In this case, a translational shake compensation amount is calculated from the imaging magnification of the imaging lens to thereby compensate image shake. Even when the amount of translational shake of the camera is the same, the compensation amount for translational shake to be compensated on the image surface varies in response to the imaging magnification since the imaging magnification constantly changes during AF operations. If shake compensation is performed without modification in accordance with information for imaging magnification obtained from a zoom or focus state, there is a risk of an effect on shake compensation effect of the shake compensation if an excessive large compensation amount is used in relation to translational shake. Furthermore, shake compensation control performance may be adversely affected when the shake compensation lens (image blur correction lens) immediately reaches a control limit (end position in a moveable range) as a result of excessive control.
The present invention has the object of reducing deterioration in shake compensation control performance caused by rapid variation in an imaging magnification produced during AF operations, and executing high accuracy image shake compensation in relation to translational shake.